Issue with using default tag with pointer type #47
Description
TL;DR: When using the mod:"default" tag with a field of type *string, if the field is nil, the library assigns it to a pointer referencing an empty string ("") instead of the defined default value.
Context:
Hi team, thank you for the great work on this library!
While integrating it into my project, I encountered an unexpected behavior and am seeking your advice.
Here’s a simplified example to illustrate the issue:
package main
import (
"context"
"fmt"
"log"
"github.com/go-playground/mold/v4/modifiers"
)
var conform = modifiers.New()
type User struct {
Name *string `mod:"default=abc"`
}
func main() {
user := User{}
fmt.Println("Name:", user.Name) // Output: nil (as expected)
err := conform.Struct(context.Background(), &user)
if err != nil {
log.Panic(err)
}
fmt.Println("Conformed Name:", *user.Name) // Output: "" (unexpected, expected "abc")
}Problem:
The Name field in the User struct is of type *string and is configured with the mod:"default=abc" tag.
However, if the field is initially nil, the library assigns it to a pointer referencing an empty string ("") instead of a pointer referencing the expected default value ("abc").
Expected Behavior:
If the Name field is nil, it should be assigned to a pointer referencing the default value ("abc") as defined by the mod:"default=abc" tag
Investigation and proposal:
I traced the issue to the following section of code in the modifiers/multi.go file:
case reflect.Ptr:
fl.Field().Set(reflect.New(fl.Field().Type().Elem()))
}This code initializes a pointer field to point to an empty value (e.g., an empty string).
However, it does not account for the configured default value defined in the mod:"default=..." tag. As a result, the pointer field ends up pointing to an empty string instead of the specified default value.
To fix this, I suggest updating the logic to use the configured default value when initializing the pointer. Here’s a proposed modification:
case reflect.Ptr:
value := fl.Param() // Retrieve the configured default value
fl.Field().Set(reflect.ValueOf(&value)) // Set the field to point to the default value
}Please let me know if this behavior is intentional or if there is a recommended way to achieve the expected behavior. Thanks in advance!